This invention relates to a fluorescent lamp, and more particularly to a dimmer switch for a fluorescent lamp.
Reference may be made to U.S. Pat. No. 4,178,535 disclosing a ballast circuit for a fluorescent lamp having a gaseous discharge light bulb and first and second ballast chokes or inductors housed in a threaded lamp base similar to that of a standard 120 V incandescent light bulb, the ballast circuit being adapted to be connected to a conventional three-way light switch housed in a 120 V light socket or lamp holder to form a dimmer switch for the lamp. In the first position of the three-way switch, the first inductor is connected in the ballast circuit in series with the light bulb while the second inductor is removed from the circuit. In the second position of the switch the second inductor is connected in the ballast circuit in series with the light bulb while the first is removed and, in the third position, a parallel combination of both inductors is connected in the ballast circuit. Because the first and second inductors individually must have an impedance which is low enough to allow a level of ballast current (e.g., a current above approximately 250 ma for a 22-watt bulb) for "starting" the light bulb, yet the parallel combination of the inductors must have an impedance which is high enough to limit the ballast current to a level (e.g., a current below approximately 550 ma for a 22-watt bulb) which will not overheat the filaments of the bulb and thus reduce the life of the bulb, the impedance values of the first and second inductors are similar. Thus, although the three-way light switch provides three different positions and three different connections of the inductors in the ballast circuit, the prior art dimmer switch is capable of producing only two different levels of light output; namely, a low level of light output when either the first or the second inductor alone is connected in the ballast circuit and a high level when the parallel combination of the inductors is connected in the ballast circuit.